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    GM 40 not working at all

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    spod2508

    Posts : 4
    Join date : 2017-12-05

    GM 40 not working at all

    Post by spod2508 on Tue Dec 05, 2017 11:18 am

    Was playing earlier and seemed fine but when I went back to it, it flashed blue for a split second and then nothing. No switches tripped in the house, lead is fine as it works with my other amp so looks like the problem is with the GM 40. Has anyone had this happen to them or have an idea of what could be causing this? Hoping it's something simple like a fuse but worried it might be more serious.

    Thanks

    Spod
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    JonnyNonsense

    Posts : 76
    Join date : 2017-06-19

    Re: GM 40 not working at all

    Post by JonnyNonsense on Wed Dec 06, 2017 6:31 am

    On any other amp I'd say maybe a tube blew, but the GM40 has TSC so shouldn't just shut down. Like you say, it might be a fuse. These things happen with amps. Don't stress, just get it looked at..
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    spod2508

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    Join date : 2017-12-05

    Re: GM 40 not working at all

    Post by spod2508 on Wed Dec 06, 2017 7:40 am

    JonnyNonsense wrote:On any other amp I'd say maybe a tube blew, but the GM40 has TSC so shouldn't just shut down. Like you say, it might be a fuse. These things happen with amps. Don't stress, just get it looked at..

    Dropping her into a local guy today. Fingers crossed it's nothing too serious.
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    bordonbert

    Posts : 1091
    Join date : 2015-01-28
    Age : 98
    Location : Southern England

    Re: GM 40 not working at all

    Post by bordonbert on Wed Dec 06, 2017 8:21 am

    There is a specific HT fuse in the old GM36 labelled FU1 which was a 20mm T400mAL250V (note that is 'T' for slow blow) and it should be about the same for the GM40. It's 400mA at 250V. It would be stamped into the fuse itself. Being in the HT side of things it's supposed to be non-user serviceable and it is definitely best left alone if you aren't used to working inside high voltage gear, but if you do have the experience and know how to open the amp without damaging the anti-tamper warranty checks it is just a standard fuse holder on the circuit board. There is also a 20mm T800mAL250V labelled FU2 for the LT side too. Don't mix the two up.

    It isn't unknown for that fuse to go out on you and it stops the amp dead in its tracks as it robs all of the valves of anode voltage HT. You ABSOLUTELY MUST get exactly the correct type as a replacement.
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    spod2508

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    Join date : 2017-12-05

    Re: GM 40 not working at all

    Post by spod2508 on Thu Dec 07, 2017 5:57 am

    bordonbert wrote:There is a specific HT fuse in the old GM36 labelled FU1 which was a 20mm T400mAL250V (note that is 'T' for slow blow) and it should be about the same for the GM40.  It's 400mA at 250V.  It would be stamped into the fuse itself.  Being in the HT side of things it's supposed to be non-user serviceable and it is definitely best left alone if you aren't used to working inside high voltage gear, but if you do have the experience and know how to open the amp without damaging the anti-tamper warranty checks it is just a standard fuse holder on the circuit board.  There is also a 20mm T800mAL250V labelled FU2 for the LT side too.  Don't mix the two up.

    It isn't unknown for that fuse to go out on you and it stops the amp dead in its tracks as it robs all of the valves of anode voltage HT.  You ABSOLUTELY MUST get exactly the correct type as a replacement.

    Not something I'd even consider going at myself. The guy I left it with came with 5-6 very strong recommendations from friends of mine covering a range of gear. He's also got some local stores operating as drop-off/pick-up points which I'm sure they wouldn't do if feedback on his work was sketchy.
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    bordonbert

    Posts : 1091
    Join date : 2015-01-28
    Age : 98
    Location : Southern England

    Re: GM 40 not working at all

    Post by bordonbert on Thu Dec 07, 2017 6:02 am

    Good stuff. Keep us up to date with what he finds.

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